Insecticidal compositions exist in a wide variety of formulations. Liquid formulations are among the most useful of these since they are convenient to handle, easily measured, quick to disperse in water, and lend themselves to low-volume applications. Liquid formulations eliminate the toxic dust problem normally associated with dry formulations. As compared to conventional solid formulations they are easier to dilute to spray volume. Liquid concentrates can be pumped; and even when used in small amounts, liquid formulations can be more conveniently and accurately measured than solid formulations.
The active insecticidal ingredient, S-methyl N-[(methylcarbamoyl)oxy]thioacetimidate, a method of making it, and a wide variety of formulations and methods for using it are disclosed in U.S. Pat. No. 3,647,861, issued Mar. 7, 1972, to James B. Buchanan. Related disclosures are found in U.S. Pat. Nos. 3,639,633 and 3,576,834 issued Feb. 1, 1972, and Apr. 27, 1971, respectively to James B. Buchanan. Included is an insecticidal composition containing 25% by weight S-methyl N-[(methylcarbamoyl)oxy] thioacetimidate dissolved in a solvent consisting of 60% by weight methanol and 40% by weight water. (In the description which follows all percents are by weight.)
Compositions containing said thioacetimidate are frequently subjected to near freezing or sub-freezing temperatures during transit or storage. When the composition is in the form of a liquid concentrate, low temperature solubility then becomes an important consideration in choosing a particular solvent system. The above-mentioned 60:40 methanol:water solvent possesses relatively low solubility for said thioacetimidate at low temperatures. For example, the solubility of said thioacetimidate in said solvent system is less than 18% at 0.degree.C. and less than 15% at -6.degree.C.
Copending U.S. Pat. application Ser. No. 317,802, filed Dec. 22, 1972 now U.S. Pat. No. 3,862,316, by Johnny Leroy Armstrong discloses liquid, water-soluble concentrated compositions of S-methyl N-[(methylcarbamoyl)oxy]thioacetimidate containing 20% to 30% of said thioacetimidate dissolved in a binary solvent consisting essentially of 80% to 95% methanol and 5% to 20% water. Such a composition gives an unexpected increase in the low temperature solubility of said thioacetimidate, but the proportion of methanol necessary to cause this desired increase in low temperature solubility will also cause the resulting composition to possess a relatively low flash point. Thus, handling of such a composition will require precautions, and a certain amount of inconvenience will result.
It would, of course, be desirable to maintain or increase the low temperature solubility while reducing the flammability hazard (i.e., increasing the flash point). Preferably, it would be desirable to maintain or increase the low temperature solubility while increasing the flash point to at least 100.degree.F. to provide a minimum flammability hazard and to eliminate the necessity for special precautions and inconvenience in handling.
Thus, a number of criteria become important in the selection of the solvent system for use in the preparation of liquid, water-soluble concentrates of S-methyl N-[(methylcarbamoyl)oxy]thioacetimidate. The thioacetimidate must have a high level of low temperature solubility in the chosen solvent system. The solvent system should have a relatively high flash point. The solvent system when admixed with the thioacetimidate must provide a homogeneous (i.e., single phase) composition. In addition, the solvent system must be safe with respect to the plants that are to be treated with the thioacetimidate composition, i.e., the solvent cannot be phytotoxic. Furthermore, the solvents must be approved by the Environmental Protection Agency for use on growing crops.
It has now been found unexpectedly that each of the above-mentioned criteria can be satisfied by the ternary and quaternary solvent systems of the present invention. In particular, it has been found unexpectedly that when sufficient S-methyl N-[(methylcarbamoyl)oxy]thioacetimidate to create a 15% to 35% solution of said thioacetimidate is dissolved in the ternary or quaternary solvent systems of the present invention at 25.degree.C. there will result a homogeneous (single phase) composition, i.e., the dissolution of said thioacetimidate in the solvent system of the present invention aids in the formation of a single phase. It has further been found that said thioacetimidate possesses an unexpectedly high level of low temperature solubility in the solvent systems of the present invention.